fix: parentheses handling in CHECK constraint normalization

internal/ir/normalize.go

@@ -849,9 +849,15 @@ func normalizeCheckClause(checkClause string) string {
 		clause = after
 	}
 
-	// Remove outer parentheses if present (may be multiple layers)
-	for strings.HasPrefix(clause, "(") && strings.HasSuffix(clause, ")") {
-		clause = strings.TrimSpace(clause[1 : len(clause)-1])
+	// Remove ONLY outer parentheses if they are balanced and not part of complex expression
+	clause = strings.TrimSpace(clause)
+	for len(clause) > 0 && clause[0] == '(' && clause[len(clause)-1] == ')' {
+		// Check if parentheses are balanced
+		if isBalancedParentheses(clause[1 : len(clause)-1]) {
+			clause = strings.TrimSpace(clause[1 : len(clause)-1])
+		} else {
+			break
+		}
 	}
 
 	// First apply legacy conversions to handle PostgreSQL-specific patterns

testdata/diff/create_table/add_check/diff.sql

@@ -0,0 +1,2 @@
+ALTER TABLE code
+    ADD CONSTRAINT code_check CHECK (code > 0 AND code < 255);

testdata/diff/create_table/add_check/new.sql

@@ -0,0 +1,3 @@
+CREATE TABLE public.code (
+    code integer PRIMARY KEY CONSTRAINT code_check CHECK (code > 0 AND code < 255)
+);

testdata/diff/create_table/add_check/old.sql

@@ -0,0 +1,3 @@
+CREATE TABLE IF NOT EXISTS code (
+    code integer PRIMARY KEY
+);

testdata/diff/create_table/add_check/plan.json

@@ -0,0 +1,26 @@
+{
+  "version": "1.0.0",
+  "pgschema_version": "1.1.0",
+  "created_at": "2025-09-23T18:49:35+03:00",
+  "source_fingerprint": {
+    "hash": "a9d472cd406e27485b570b72906ad224b8282469bd50699bddd6da04acdabaef"
+  },
+  "groups": [
+    {
+      "steps": [
+        {
+          "sql": "ALTER TABLE code\nADD CONSTRAINT code_check CHECK (code > 0 AND code < 255) NOT VALID;",
+          "type": "table.constraint",
+          "operation": "create",
+          "path": "public.code.code_check"
+        },
+        {
+          "sql": "ALTER TABLE code VALIDATE CONSTRAINT code_check;",
+          "type": "table.constraint",
+          "operation": "create",
+          "path": "public.code.code_check"
+        }
+      ]
+    }
+  ]
+}

testdata/diff/create_table/add_check/plan.sql

@@ -0,0 +1,4 @@
+ALTER TABLE code
+ADD CONSTRAINT code_check CHECK (code > 0 AND code < 255) NOT VALID;
+
+ALTER TABLE code VALIDATE CONSTRAINT code_check;

testdata/diff/create_table/add_check/plan.txt

@@ -0,0 +1,16 @@
+Plan: 1 to modify.
+
+Summary by type:
+  tables: 1 to modify
+
+Tables:
+  ~ code
+    + code_check (constraint)
+
+DDL to be executed:
+--------------------------------------------------
+
+ALTER TABLE code
+ADD CONSTRAINT code_check CHECK (code > 0 AND code < 255) NOT VALID;
+
+ALTER TABLE code VALIDATE CONSTRAINT code_check;